An efficient synthesis of 3-trifluoromethylated 8-oxabicyclo[3.2.1]octa-2,6-dienes

The rhodium(II) acetate catalyzed decomposition of 3-trifluoromethylated vinyldiazomethanes 3 in the presence of furans resulted in the formation of a series of 3-trifluoromethylated 8-oxabicyclo[3.2.1]octa-2,6-dienes. The 4-substituent on the vinyldiazomethanes had great effects on the product distribution and the stereo- and regiochemistry of the [3+4] annulation products. The rhodium(II) acetate catalyzed reaction of 4-carbonyl substituted vinyldiazomethanes 3a–c with furans resulted in cyclopropenes and [3+4] annulation products, while in the case of cyano-substituted vinyldiazomethanes 3d, only cycloaddition products were obtained. The reaction was presumed to follow a tandem cyclopropanation/Cope rearrangement mechanism.